U.S. Pat. No. 6,617,211 discloses a memory integrated circuit and a method of fabricating a crown-cell capacitor for memory integrated circuits. The circuit comprises a multilayer structure with a plurality of conductive layers which are insulated from another by insulating layers. In order to connect the integrated circuit externally, conductive pads are arranged on top of the circuit. The conductive pads are separated from the uppermost conductive layer by a dielectric material.
In order to minimize the production costs of semiconductor devices, their size is kept as small as possible. The thickness of all layers of the semiconductor device is chosen as thin as possible to minimize process time of deposition. As a result for the lateral and vertical minimization, the mechanical robustness of the devices is reduced. If, for example, probe needles are placed on top of the conductive pads in order to test the electrical behavior of the device, the mechanical force applied to the pads, may not be too large. If the mechanical force exceeds a certain value, the insulating material—i.e., the dielectric material between the conductive pad and the uppermost conductive buried layer or the dielectric material in-between the conductive buried layers—may break and internal cracks may result. Usually, these cracks do not destroy the device at once. However, they may result in a reduced device's lifetime and reliability in terms of product functionality. For instance, due to lacking diffusion barriers for copper, migration process starts and conductive material may migrate through the barrier-crack or/and along the cracks through the insulating material and may cause electrical short-circuits between isolated conducting wires.
In order to solve this problem, prior art devices usually do not use the area below conductive pads for buried conductive layers. In prior art devices, the space below these pads is electrically inactive in order to avoid short-circuits due to mechanical cracks. This space could consist of pure dielectric material without any structures. Another possibility is to fill the space up with periodic structures for unit process reasons. In all cases the space under the pads are not used for functional electrical wiring.